The offshore drilling industry is going to deeper water, introducing new challenges. Deep water with low water temperature in combination with high pressure increases the risk of hydrates. Some fields like the pre-salt reservoir outside Brazil and the Gulf of Mexico have got challenging wells with very little drilling margin, (difference with pore pressure and fracture pressure). Drilling in fractured carbonate is also a challenge for the industry. These types of wells often experience lost circulation cases and sometimes in combination with gas kicks. When lost circulation is experienced, lost circulation material (LCM) or other sacrificial fluids can be pumped down the well in large quantities which will cool down the well, increasing the hydrate risk. Use of pressurized mud cap drilling or dual mud cap drilling increase also risk of hydrates since often large amount of water is used to pump down the well. The introduction of managed pressure drilling (MPD) increase also the risk of hydrates in riser, since the riser will see a higher pressure compared with conventional drilling.
Hydrates may plug subsea BOP (typically below annular preventer) and subsea kill and choke lines. Several case histories and papers about plugged kill and choke lines and other hydrate issues have been published. With introduction of special dual gradient managed pressure drilling MPD system with annular preventer installed subsea in the drilling riser and conventional MPD with riser drilling device (RDD), the risk of plugging outlets from the drilling riser also increases.